CVD of PtRh with good adhesion and morphology

ABSTRACT

A method and system for performing metal-organic chemical vapor deposition (MOCVD). The method introduces a metal-organic compound into the CVD chamber in the presence of a first reactant selected to have a reducing chemistry and then, subsequently, a second reactant selected to have an oxidizing chemistry. The reducing chemistry results in deposition of metal species having a reduced surface mobility creating more uniform coverage and better adhesion. The oxidizing species results in deposition of metal species having a greater surface mobility leading to greater surface agglomeration and faster growth. By alternating the two reacts, faster growth is achieved and uniformity of the metal structure is enhanced.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 09/997,073filed Nov. 18, 2001 and is hereby incorporated in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor processing and, inparticular, concerns a chemical vapor deposition (CVD) technique forforming conductive layers, such as platinum-rhodium layers, in a mannerthat results in better adhesion of the component layer on the surface ofa semiconductor device and better morphology of the layer.

2. Description of the Related Art

Modern semiconductor chemical vapor deposition (CVD) technology hasprovided fabrication procedures for the development of VLSI(Very-Large-Scale Integration) and ULSI (Ultra-Large-Scale Integration)circuitry. Even though the number of surface mounted semiconductordevices has significantly increased, the surface density is oftenlimited by the finite quantity of real estate on the semiconductor wafersurface. As a result, the finite surface density limitation has inducedgrowth in the vertical direction of modern semiconductor devices. Thisoften requires multiple levels of the conductive interconnects thatoften, in turn, require numerous metallic-based deposition layers.

As the size of the conductive elements has decreased to accommodatehigher density of components, many conventional semiconductor processingtechniques for forming conductive elements are forming conductiveelements that exhibit more gaps and pinholes and poorer adhesion to thesubstrate. One particular CVD deposition technique utilized for formingconductive elements is Metal-organic Chemical Vapor Deposition (MOCVD).However, conventional MOCVD techniques alone cannot always compensatefor the relatively poor adhesion and morphology that occurs in smallerdevices.

For example, complex chemical reactions that occur during the formationof semiconductor devices dictate the final composition of the depositedlayer, which may be different than the intended composition.Specifically, the grain structure within the deposited layer may varydepending on the growth rate and the growth environment during themanufacturing and deposition process. A variance in the grain size andgrain structure within deposited layers of similar composition andthickness may interfere with or alter the conduction characteristics ofelectrical current flow through the grain interfaces.

A typical MOCVD technique is as follows. A precursor gas, comprising atleast one conductive component or element, and other reactants areintroduced into a CVD chamber, and the conductive element carried by theprecursor gas is then deposited onto the semiconductor surface of thesemiconductor substrate through thermal decomposition. The precursor gasmay often be a metal-organic compound, wherein conductive atoms may bebonded to organic compounds, which allows the conductive atoms to betransferred to the semiconductor surface in a gas phase. This enablesthe conductive atoms, such as platinum and rhodium, to be deposited overthe surface of the semiconductor substrate surface as the metal-organiccompound facilitates conventional step coverage.

In the prior art, there is generally only a single deposition step suchthat the precursor gas is introduced into the CVD chamber until enoughconductive molecules have been deposited on the exposed semiconductorsurface to form a conductive element of a desired thickness. However, asdiscussed above, conventional MOCVD techniques can result in pooradhesion and poor morphology of the deposited conductive element. Thisproblem is exacerbated in higher density applications requiring smallerconductive components.

From the foregoing, it will be appreciated that there is a need for animproved conductive layer processing technique for depositing, in oneembodiment, conductive materials onto a semiconductor substrate surfacesuch that improved substrate adhesion and improved morphology may beobtained without a significant increase in the cost of manufacturing theconductive film layer. To this end, there is also a need for a moreefficient method of depositing conductive elements, such as platinum andrhodium, in a manner that exhibits an improved grain interface structureand greater compositional uniformity.

SUMMARY OF THE INVENTION

The aforementioned needs are satisfied by the present invention which,in one aspect is comprised of a method of forming a conductive layer ona substrate. In this aspect, the method comprises positioning thesubstrate in a chemical vapor deposition (CVD) chamber and thenintroducing at least one precursor gas, having at least one conductivecomponent and at least one organic component, into the CVD chamber. Afirst reactant gas is then introduced into the chamber so as todisassociate the at least one conductive component from the at least oneorganic component at one activation energy so as to result in a firstlayer of conductive material being formed on the substrate. A secondreactant gas is then introduced into the chamber after introducing thefirst reactant gas so as to disassociate the at least one conductivecomponent from the at least one organic component at another activationenergy greater than the first energy so as to result in columnar growthsof conductive material from the first layer of the conductive materialformed on the substrate. The method further comprises re-introducing thefirst reactant gas into the chamber so as to planarize the conductivefilm by filling in gaps between the columnar growths of the conductivematerial.

In one embodiment, the first reactant gas is a reducing gas and thesecond reactant gas is an oxidizing gas. The use of the reducing gasresults in reduced surface mobility of the atoms which results ingreater step coverage and promotes better adhesion. The periodic use ofthe oxidizing gas results in greater surface mobility causing the atomsto agglomerate together which promotes faster columnar growths. Theperiodic reintroduction of the first reactant gas, however, results inbetter filling in of the gaps and pin holes resulting from the fastercolumnar growths. In one specific embodiment, the at least one precursorgas is a mixture of gases, which comprises platinum, rhodium, or acombination thereof. In another specific embodiment, a plurality ofprecursor gases may be used, wherein a first precursor gas comprises aplatinum component and a second precursor gas comprises a rhodiumcomponent.

In another aspect of the invention, the invention comprises a method offorming a conductive structure on a semiconductor substrate. The methodcomprises (i) performing a first metal-organic chemical vapor depositionstep using a first chemistry selected to provide more uniform coverageof the semiconductor substrate and (ii) performing a secondmetal-organic chemical vapor deposition step using a second chemistryselected to provide for increased columnar growth. The method furthercomprises alternating the acts (i) and (ii) until a conductive structureof a pre-selected thickness is formed on the semiconductor substrate sothat the performance of the first metal-organic chemical vapordeposition act decreased gaps and pin holes formed during theperformance of the second metal-organic chemical vapor deposition act.

In yet another aspect of the invention, the invention comprises a systemfor forming a conductive element on a semiconductor device. The systemcomprises a CVD chamber that receives the semiconductor device. Thesystem also includes a precursor gas supply system that provides atleast one precursor gas to the CVD chamber, wherein the at least oneprecursor gas comprises conductive components that when deposited on thesemiconductor device form the conductive element and organic componentswhich facilitate step coverage of the conductive element over thesemiconductor device. The system also includes a reactant gas supplysystem that provides both a first reactant and a second reactant intothe chamber so that the precursor gas is deposited using both a firstchemistry and a second chemistry such that the first chemistry providesmore uniform step coverage and the second chemistry provides increasedvertical growth of the conductive element, which is comprised by the atleast one precursor gas, on the semiconductor substrate.

The aspects of the present invention result in a process or system forforming conductive elements that is both efficient and leads to improvedmorphology and adhesion. These and other objects and advantages willbecome more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system block diagram, whichdepicts one embodiment of a deposition system for the formation of aconductive structure on a semiconductor device;

FIGS. 2A-2E are cross-sectional views of a semiconductor deviceillustrating one embodiment of a method, whereby a conductive structureis formed on the semiconductor device;

FIG. 3A is a graphical illustration of a typical platinum precursor gasmolecule used in a CVD process;

FIG. 3B is a graphical illustration of a typical rhodium precursor gasmolecule used in a CVD process;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made to the drawings wherein like numerals referto like parts throughout. FIG. 1 is a block diagram of one embodiment ofa deposition system 100 for the formation of a conductive structure orelement of the present invention. As is illustrated in FIG. 1, achemical vapor deposition (CVD) chamber 102, of a type known in the art,is supplied with precursor gases 104 a, 104 b that is utilized todeposit conductive layers and structures on semiconductor devicespositioned within the CVD chamber 102. In particular, a carrier gas 106from a carrier gas source 116 is supplied to a bubbler 114, which, inthis embodiment, comprises a first metal-organic liquid precursor 108and a second metal-organic liquid precursor 110.

Additionally, the carrier gas 106 is utilized to carry the vapor of theconductive metal-organic components comprised by the liquid precursors108 and 110. Furthermore, a first metal-organic precursor gas 104 adevelops from the first metal-organic liquid precursor 108, and a secondmetal-organic precursor gas 104 b develops from the second metal-organicliquid precursor 110. In one embodiment, the precursor gases 104 a, 104b may be introduced separately, in either a simultaneous manner or atpre-determined temporal intervals, to the CVD chamber 102 in a mannerknown in the art. In another embodiment, the precursor gases 104 a, 104b may be mixed within the bubbler chamber 122 so as to form a precursorgas mixture that may then be introduced to the CVD chamber 102 in amanner known in the art.

In one preferred embodiment, the carrier gas 106 is a known helium-basedinert gas, which serves to carry the vapor of the liquid precursors 108and 110. The inert helium-based carrier gas 106 is supplied to thebubbler 114, which houses the first metal-organic liquid precursor 108,such as, for example, methylcyclopentadienyl trimethyl platinum(MeCpPtMe₃) (See, FIG. 3A), and the second metal-organic liquidprecursor 110, such as, for example, Dicarbonyl Cyclopenda DienylRhodium (DCDR)(See, FIG. 3B). The carrier gas 106 carries the vapor ofthe liquid precursors 108 and 110, which may comprise the platinum-basedmetal-organic components and the rhodium-based metal-organic components.In one aspect, the platinum-based metal-organic vapor and therhodium-based metal-organic vapor may then be mixed in the bubblerchamber 114 and subsequently introduced to the CVD chamber 102 for apre-selected period of time so as to allow the conductive metal-organiccomponents to coat the semiconductor device via chemical vapordeposition techniques. In another aspect, the first precursor gas 104 a,such as the platinum-based metal-organic vapor, and the second precursorgas 104 b, such as the rhodium-based metal-organic vapor, may beseparately introduced to the CVD chamber 102 for a pre-selected periodof time so as to allow the conductive metal-organic components to coatthe semiconductor device via chemical vapor deposition techniques.

While in this particular embodiment, the metal-organic precursor gases104 a, 104 b have platinum-based and/or rhodium-based components, itwill be appreciated that any of a number of different precursor gasesand/or vapors may be used without departing from the scope of thepresent invention. These metal-organic gases and/or vapors include, butare not limited to, gases and/or vapors that entrain conductive elementssuch as Pt, Rh, Ir, Ni, Co, Cu, W, and the like or any combinationthereof.

As is also illustrated in FIG. 1, the deposition system 100 includes afirst reactant source 122 that provides a first reactant vapor 126 and asecond reactant source 124 that provides a second reactant vapor 128into the CVD chamber 102 that are alternatively selected so as tointeract with the conductive metal-organic compounds of the precursorgases 104 a, 104 b to thereby facilitate more a more uniform andefficient deposition of the conductive metal-organic molecules comprisedby the precursor gases 104 a, 104 b. Providing the reactant vapors, 126and 128, into the CVD chamber 102 allows the metal-organic moleculescomprised by the precursor gases 104 a, 104 b to deposit on the surfaceof the semiconductor device that is positioned within the CVD chamber102. As is also illustrated in FIG. 1, the illustrated chemical vapordeposition system 100 also includes a waste gas receptacle 130 thatreceives waste gas 132, which may comprise unused precursor gases 104 a,104 b, unused reactant vapors, 126, 128, and other reaction by-productsproduced during the CVD process. In the preferred CVD process, the firstreactant vapor 126 is a reducing agent, such as diatomic hydrogen or ahydrogen derivative (H₂), and the second reactant vapor is an oxidizingagent, such as diatomic oxygen or an oxygen derivative (NO, N₂O, O₂, orO₃).

FIGS. 2A-2E are cross-sectional views of a semiconductor device 200depicting one embodiment of a deposition process and method of theillustrated embodiment in greater detail, whereby a conductive structureis formed on the semiconductor device 200. As is illustrated in FIG. 2A,a semiconductor device 200, which may comprise a semiconductor substrate202 with a surface 204, is positioned within the CVD chamber 102. Theprecursor gases 104 a, 104 b are introduced into the CVD chamber 102such that a conductive material, such as platinum-rhodium (PtRh), isdeposited on the exposed surface 204 of the semiconductor device 200.The deposition process begins with a nucleation process, whereinnucleation sites develop as the first few metal-organic molecules aredeposited onto the semiconductor substrate surface 204. The nucleationprocess involves the first reactant vapor 126, which is simultaneouslyintroduced into the CVD chamber 102 along with the precursor gases 104a, 104 b. The first reactant vapor 126 is preferably selected to serveas a reducing agent that reacts with the precursor gases 104 a, 104 b.Additionally, the resulting reduction chemistry may offer a more uniformnucleation on the semiconductor substrate surface 204, which maypossibly be due to its comparatively low reaction energy andcomparatively resulting low surface mobility. In one particularembodiment, the first reactant vapor 126 includes a hydrogen based gas,such as a gas selected from the group of H₂, NH₃ or H₂O.

The comparatively low reaction energy may provide for a comparativelylow surface mobility as the metal-organic molecules adhere more readilyto the semiconductor surface 204 with less surface movement and lesstendency to agglomerate together. The low reaction energy, the lowsurface mobility, and the low deposition rate of the reduction chemistrymay provide increased uniformity and less agglomeration, which may leadto better adhesion of the conductive film layer during the nucleationprocess stage. Good adhesion during the initial stage of the conductivefilm formation process produces a semiconductor device film layer withless internal defects, which serves to improve the functionality,integrity, and reliability of the device. Also, residual hydrogenbonding of conductive elements to the semiconductor substrate surfacemay also contribute to the good nucleation adhesion.

FIG. 2B graphically illustrates the results of further growth of theinitial nucleation sites. After the nucleation process is complete, thefirst reactant vapor 126 is no longer introduced into the CVD chamber102. Instead, the second reactant vapor 128 is simultaneously introducedinto the CVD chamber 102 along with the precursor gases 104 a, 104 b.The second reactant vapor 128, in one embodiment, serves as an oxidizingagent that reacts with the precursor gases 104 a, 104 b, and, due to itshigh reaction energy, the applied oxidation chemistry results in rapidcolumnar growths 208 above the initial nucleation sites that weredeposited with reduction chemistry on the semiconductor substratesurface 204. The high reaction energy state may provide for an increasedsurface mobility as the metal-organic molecules begin to adhere to thesemiconductor surface 204 which results in the metal atoms agglomeratingtogether into the columns. The fast columnar growth tends to leave gaps210 and pinholes 212 between the grain structures of the conductiveelements. These flaws may be corrected with the application of anotherreduction chemistry process, which will be further described hereinbelow. In one embodiment, the second reactant vapor 128 is comprised ofan oxygen containing gas such as N₂O, O₂, NO or O₃.

FIG. 2C graphically illustrates the subsequent processing—step ofrepeating the application of reduction chemistry to the semiconductordevice 200. After the oxidation layer 208 is complete, the secondreactant vapor 128 is no longer introduced into the CVD chamber 102,but, instead, the first reactant vapor 126 is introduced into the CVDchamber 102 along with the introduction of the precursor gases 104 a,104 b. Due to the lower reaction energy and the resulting lower surfacemobility of depositing conductive elements with reduction chemistry,inserting a conductive layer deposited with reduction chemistryinterposed between two conductive layers deposited with oxidationchemistry may serve to disrupt the grain structure in the directionnormal to the semiconductor surface 204. In addition, the slowdepositions rates of reduction chemistry may tend to fill in the gapsand pinholes left by the rapid growth rates of oxidation chemistry.

FIG. 2D graphically illustrates that the next layer of oxidationchemistry will grow more uniformly. As is illustrated in FIG. 2D, theuse of the oxidation chemistry by the introduction of the secondreactant vapor 128, results in quicker growth of the thin film layer, asdiscussed above. However, as is illustrated in FIG. 2E, alternatingreduction and oxidation chemistry processes results in an improved grainstructure as a result of the reducing chemistry filling in more of thegaps and pin holes. The process of alternating reduction and oxidationchemistries may be repeated until the desired thickness of theconductive layer is achieved.

The advantage of utilizing reduction chemistry for the initialnucleation phase is the reduced surface mobility of the metallicmolecules, such as platinum, rhodium, and/or a combination thereof. Areduced surface mobility of the metallic molecules results in a moreuniform coverage of the semiconductor surface 204, improved adhesion andimproved morphology of the metallic molecules onto the semiconductorsurface 204. The uniform coverage is the result of less agglomeration ofthe metallic molecule during the reduction chemistry phase of the MOCVDprocess, which results in a reduction of gaps and pinholes in theconductive film layer. Additionally, there may also be some residualhydrogen bonding between the substrate molecules and the metallicmolecules, which may also contribute to the improved adhesion of themetallic molecules onto the semiconductor substrate surface.

Furthermore, the advantage of utilizing oxidation chemistry after thereduction chemistry is that oxidation reactions involve higher reactionenergies, which result in an increased surface mobility of the metallicmolecules, such as platinum and rhodium. The higher reaction energy ofthe metallic molecules increases the agglomeration rate, which resultsin a rapid columnar growth rate. Although the rapid growth rate maycause poorer adhesion and morphology, such that gaps and pinholes in thefilm layer more readily occur, the addition of another reduction filmlayer interposed between two oxidation layers tends to reduce theproblems of poorer adhesion morphology.

Another advantage to alternating the reduction and oxidation chemistriesis that reduction contaminates, such as carbon, left behind by themetal-organic reduction reactions may be burned out of the conductivefilm layer during the oxidation process, which improves the overallpurity and cohesion of the metallic molecules to each other and to thesemiconductor surface. Additionally, the process of alternating thereduction and oxidation chemistries produces metal-organic depositionlayers that exhibit the ability to maintain a uniform topography,wherein the deposited layers have a substantially flat and smoothsurface. The improved morphology results in the reduction of surfacedefects, such as step layer thinning, cracks, and surface reflections.

In one particular example of the above process, a conductive layer 220is formed using an initial deposition step, wherein a platinum-rhodiumprecursor carrier gas is provided from the conductive carrier gas source116 through the bubbler 114 at a rate of between 5 to 300 sccm with theplatinum-rhodium being encapsulated within a helium carrier. The bubbler114 contains a liquid precursor at a temperature between 20° C. and 200°C., such that the resulting precursor gases 104 a, 104 b emanating fromthe bubbler 114 has the chemical composition as illustrated in FIGS. 3Aand 3B. The resulting precursor gases 104 a, 104 b is provided from thebubbler 114 to the CVD chamber 102 along with an initial simultaneousintroduction of H₂ reactant 126 at a rate of 50 to 1000 sccm from thereactant source 122. This introduction of precursor gases 104 a, 104 band reactant 126 is provided to the CVD chamber 102 for approximately 50seconds to result in deposition of the nucleation sites 206. At the endof the approximately 50 second nucleation period, the introduction ofthe precursor gases 104 a, 104 b from the bubbler 114 is continued whilethe introduction of the N₂O reactant 128 from the reactant source 124 iscontinued for approximately 50 seconds. The N₂O thus comprises thereactant 128, which reacts with the metal-organic compounds comprised bythe precursor gases 104 a, 104 b in the deposited layer 160 to furthergrow the conductive layer 220. These two process steps are alternatelyrepeated until a conductive layer or element of a desired thickness isformed.

From the foregoing, it will be appreciated that the above-describedmetal-organic chemical vapor deposition process illustrates a method offorming a conductive film layer 220 or structure on a semiconductordevice 202 that results in a more uniform conductive film structure withimproved adhesion and morphology. This results in a significantlyefficient conductive device that exhibits improved conduction and lessresistivity between grain interfaces. Moreover, the improvedefficiencies may also result in faster devices that exhibit improvedreliability and functionality overall.

Although the foregoing description of the preferred embodiment of thepresent invention has shown, described and pointed out the fundamentalnovel features of the invention, it will be understood that variousomissions, substitutions and changes in the form of the detail of theapparatus as illustrated as well as the uses thereof, may be made bythose skilled in the art without departing from the spirit of thepresent invention. Consequently, the scope of the present inventionshould not be limited to the foregoing discussions, but should bedefined by the appended claims.

1. A system for forming a conductive element on a semiconductor device,the system comprising: a CVD chamber that receives the semiconductordevice; a conductive precursor gas supply system that provides aconductive precursor gas to the CVD chamber wherein the conductiveprecursor gas has both conductive components that when deposited on thesemiconductor device form the conductive element and organic componentswhich facilitate step coverage of the conductive element over thesemiconductor device; and a reactant gas supply system that providesboth a first reactant and a second reactant into the chamber so thatconductive precursor gas is deposited using both a first chemistry and asecond chemistry such that the first chemistry provides more uniformstep coverage and the second chemistry provides increased verticalgrowth of conductive element and the semiconductor substrate.
 2. Thesystem of claim 1, wherein the conductive precursor gas supply systemprovides a metal-organic gas to the CVD chamber.
 3. The system of claim2, wherein the conductive precursor gas supply system provides acombination of Methylcyclopentadienyl Trimethyl Platinum gas and aDicarbonyl Cyclopentadienyl Rhodium gas.
 4. The system of claim 2,wherein the reactant gas supply system provides a first reactant that iscomprised of a reducing gas and a second reactant that is comprised of aoxidizing gas.
 5. The system of claim 4, wherein the reactant gas supplyprovides a hydrogen-based reducing gas and an oxygen-based oxidizinggas.